Perfluorooctanoate (PFOA) is a simple 8-member carbon molecule that is combined with fluorine molecules. The end result is a chemical that resembles simple forms of fat that occur naturally in our bodies or the environment, but that do not break down to any significant extent. Although PFOA does not occur naturally in the environment, it is very useful (e.g., fire-fighting foam) and stable, and as a result very low concentrations are found in the environment in many places with a few places having much higher levels that may be harmful to our health.

One way governments protect our health from harmful PFOA exposures is to develop a safe or low-risk dose, essentially a dose of PFOA to which we can all be exposed during our lifetimes without experiencing any harmful effects. This dose is determined by qualified scientists after all available and appropriate studies are reviewed. Most of these studies are done in laboratory (experimental) animals, but when human exposures occur these are also considered. These safe or low-risk doses go by various names, for example, the Reference Dose (RfD) of the U.S. Environmental Protection Agency (EPA) (Barnes and Dourson, 1988).

Several safe or low-risk doses have been estimated for PFOA by different governments. Unfortunately, these safe doses differ widely. This is due in part because scientists have not agreed on PFOA’s critical effect, which scientists define as the first effect judged to be harmful at the lowest dose. For example, US EPA (2016) judges the critical effect to be fetal toxicity in mice exposed during pregnancy. The European Food Safety Authority (EFSA, 2018) judges the critical effect to be an increase in serum total cholesterol in humans.

However, another, and perhaps more important reason for the disagreement among governments is that many scientists assume that the critical effect of PFOA is due to the length of time it takes to clear PFOA from our bodies (i.e., its half-life) rather than due to its peak concentration in blood (i.e., its maximum concentration or Cmax) (Health, 2019). For example, EPA assumed that the critical effect used to develop its safe dose for PFOA was due to its half-life and not its Cmax. Scientists associated with Toxicology Excellence for Risk Assessment (TERA) are not so sure (TERA, 2018). Thus, it has become important to consider whether the critical effect of PFOA is due to its half-life or its Cmax.

In this regard, a preliminary research case study is being proposed at a Beyond Science and Decisions workshop in February 2019. Here, half-life and Cmax information are compiled from experimental (laboratory) work in mice described by Lau et al. (2006) and Lou et al. (2009), and compared with new half-life and Cmax information found in humans exposed to PFOA as part of a cancer clinical trial (Elcombe et al., 2013, Convertino et al., 2018). Although human populations are generally exposed to much lower levels of PFOA than those used in these experimental animals or clinical human studies, the comparison of half-life and Cmax values between these studies are in agreement with current guidelines of IPCS (2005) and EPA (2014).

Safe or low-risk doses for PFOA and related chemicals by various governments are currently widely disparate. Fortunately, recent findings in humans may reduce some of this disparity. Efforts to use this newer information should allow for harmonization, or at least more consistency, in government positions.

Michael L. Dourson, PhD, DABT, FATS, FSRA, is a member of the American Council on Science and Health Board of Scientific Advisors. He has a PhD in toxicology from the University of Cincinnati, College of Medicine, and is a board-certified toxicologist (i.e., DABT) serving as the Director of Science at the 501c3 environmental science NGO, Toxicology Excellence for Risk Assessment (TERA). Prior to this, he was Senior Advisor in the Office of the Administrator at the US EPA. Before this, he was a Professor in the Risk Science Center at the University of Cincinnati, College of Medicine and also worked at TERA and US EPA.

He has been awarded the Arnold J. Lehman award from the Society of Toxicology, the International Achievement Award by the International Society of Regulatory Toxicology and Pharmacology, and 4 bronze medals from the U.S. Environmental Protection Agency. He has been elected as a Fellow of the Academy of Toxicological Sciences (i.e., FATS) and as a Fellow for the Society for Risk Analysis (i.e., FSRA).

He has co-published more than 150 papers on risk assessment methods or chemical-specific analyses, and co-authored well over 100 government risk assessment documents, many of them risk assessment guidance texts. He has made over 150 invited presentations to a variety of organizations, and has chaired over 150 sessions at scientific meetings and independent peer reviews. He has been elected to multiple officer positions in the American Board of Toxicology (including its President), the Society of Toxicology (including the presidency of 3 specialty sections), the Society for Risk Analysis (including its Secretary), and is currently the President of the Toxicology Education Foundation, a nonprofit organization with a vision to help our public understand the essentials of toxicology. In addition to numerous appointments on government panels, such as EPA’s Science Advisory Board, he is a current member on the editorial board of Regulatory Toxicology and Pharmacology and Human and Experimental Toxicology.

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